Introduction

EVM is used as a measure of the received signal constellation error. EVM is defined as the difference between the ideal received waveform and the measured waveform for allocated resource blocks. The average EVM is measured at two locations in time (low and high), where the low and high locations correspond to the alignment of the FFT window within the start and end of the cyclic prefix. LTE Toolbox requires the low and high locations to be specified as a fraction of the cyclic prefix length.

A User Equipment (UE) transmission is created using a Reference Measurement Channel (RMC) and random Physical Uplink Shared Channel (PUSCH) data and impaired by introducing additive noise to model transmitter EVM, and frequency and IQ offsets. The transmitted waveform is synchronized before the function computing EVM and in-band emissions.

Transmitter

To generate the RMC the function lteRMCUL creates a configuration structure for given UE settings specific to a given Fixed Reference Channel (FRC). This structure is used by lteRMCULTool to generate a UE transmission with random PUSCH data.

Perform Measurements

The EVM results and absolute in-band emissions for each and slot number are displayed. is the starting frequency offset between the allocated resource block (RB) and the measured non-allocated RB, i.e. for the first adjacent RB outside of the allocated bandwidth. A number of plots are also produced:

EVM versus OFDM symbol

EVM versus subcarrier

EVM versus resource block

EVM versus OFDM symbol and subcarrier (i.e. the EVM resource grid)

Note that the EVM measurement displayed at the command window is only calculated across allocated PUSCH resource blocks, in accordance with the LTE standard. The EVM plots are shown across all resource blocks (allocated or unallocated), allowing the in-band emissions to be viewed. In unallocated resource blocks, the EVM is calculated assuming that the received resource elements have an expected value of zero.

The EVM of each E-UTRA carrier for QPSK/BPSK, 16QAM, 64QAM and 256QAM modulation should not exceed the EVM level of 17.5%, 12.5%, 8% and 3.5% respectively as per TS 36.101 Table 6.5.2.1.1-1 [ 1 ].